function hasChildpage() {
	$page = wp_list_pages('depth=1&child_of=' . $post->ID . '&echo=0');

	if($page) {
		return true;
	} else {
		return false;
	}
}

http://awesomewordpressthemes.net/wordpress-tips/check-current-page-subpage/

You may want to create navigation where the children are displayed only when the parent page is the current page.  Place the code in your functions.php file

Check if current page has subpage

wordpress

PHP